A comparative study on millimeter-scale flame jet and detonation diffraction in a rectangular chamber

An experiment on high-speed turbulent flame jet and detonation diffraction in a rectangular chamber is conducted in this study. Smooth tubes with 6 mm inner diameter and different lengths are used as pre-detonators. The gaseous mixture is ethylene/oxygen with nitrogen diluted filling uniformly in both the pre-detonator and the main chamber. Flame propagations in the chamber and the velocities are observed and measured by a high-speed camera. The results show that overdriven detonation in the pre-detonator is crucial to the detonation re-initiation, which validates the argument of previous researcher’s. However, we further observed and distinguished four kinds of detonation re-initiation modes by changing the dilution ratio and the tube length. It is experimentally proved that if the overdriven detonation point is close to the exit of the pre-detonator, not only detonation re-initiation would be strengthened, but also direct initiation might possibly occur, even if the transmission ratio k is smaller than the critical value kc. The DDT distance in the chamber and the velocity characterizations are also found to be greatly affected by the flame propagation conditions in the pre-detonator.